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Tarantino, M.1, 2; Despotovic, J.3; Grainger, J.4, 5, 6, 7; Cooper, N.8, 9; Beam, D.10; Raj, A.11; Maschan, A.12; Kim, J.13; Eisen, M.13

doi: 10.1097/01.HS9.0000561040.46292.f8
Poster Session I: Platelets disorders

1The Bleeding and Clotting Disorders Institute

2University of Illinois College of Medicine-Peoria, Peoria IL

3Texas Children's Hematology Center, Houston TX, United States

4Department of Haematology, Royal Manchester Children's Hospital

5Faculty of Medical & Human Sciences, University of Manchester

6Central Manchester University Hospitals NHS Foundation Trust

7Manchester Academic Health Science Centre, Manchester

8Department of Haematology, Hammersmith Hospital

9Imperial College, London, United Kingdom

10Cook Children's Medical Center, Fort Worth TX

11Pediatric Cancer and Blood Disorders Clinic, Louisville KY, United States

12Dmitry Rogachev National Research Center for Pediatric Hematology, Oncology and Immunology, Moscow, Russian Federation

13Amgen Inc., Thousand Oaks CA, United States

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Romiplostim is approved for use in patients 1 year of age or older with ITP for ≥6 months (USA) or chronic ITP (EU) who are refractory to other treatments. Comprehensive data are needed for romiplostim use in children with persistent ITP (6-12 months) or chronic ITP (>1 year).

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To examine romiplostim safety and efficacy across trials in children with ITP.

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Data were combined from a placebo-controlled phase 1/2 trial (n = 22; Bussel Blood 2011), a placebo-controlled phase 3 trial (n = 62; Tarantino Lancet 2016), a 3-year phase 3 trial (n = 204; Grainger ASH 2017), and 2 extension trials (Bussel PBC 2015; Tarantino ASH 2017). Controlled trials and 3-year trial enrolled children <18 years with ITP for ≥6 months and ≥1 prior ITP therapy. Extension trials enrolled patients from controlled trials. Romiplostim was titrated (1-10 μg/kg/week in most trials) to maintain platelet count 50-200x109/L.

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The 286 treated patients (initially placebo, 24; romiplostim, 262) had a median age of 10 years, ITP duration of 1.9 years, and baseline platelet count of 14x109/L. Of 282 patients exposed to any romiplostim, including 20 after placebo, 69 (24%) had ITP for 6-12 months (persistent ITP) and 213 (76%) had ITP for >1 year (chronic ITP) at baseline. Median duration of romiplostim treatment was 65 weeks (persistent ITP, 65 weeks; chronic ITP, 66 weeks), including >48 weeks for 62% of patients, and median dose was 6.6 μg/kg/week. After starting romiplostim, 24% (persistent ITP, 17%; chronic ITP, 27%) had a serious adverse event (AE), most commonly epistaxis (6%). Bleeding AEs were reported for 68% of patients (persistent ITP, 65%; chronic ITP, 69%), including 10% with grade ≥3 bleeding and 2 patients with grade ≥4 bleeding. Seven patients had postbaseline neutralizing antibodies against romiplostim (2 transient). No patient had neutralizing antibodies against endogenous thrombopoietin. One patient had an increase in modified Bauermeister bone marrow grade from 0 to 2 (fine reticulin fiber network) with no associated AE, platelet count ≥30x109/L, and no follow-up biopsy. Among patients with bone marrow biopsy in the ongoing 3-year trial (Year 1, n = 27; Year 2, n = 5), there were no findings of collagen or bone marrow abnormalities vs baseline. Overall, 89% of romiplostim-treated patients (persistent ITP, 88%; chronic ITP, 90%) and 8% receiving placebo had a platelet response (≥50x109/L). Median time to platelet response for romiplostim was 6 weeks (persistent ITP, 5 weeks; chronic ITP, 6 weeks). Median platelet counts remained between 50 and 200x109/L with weekly romiplostim treatment and dose titration. Median time per month with platelet response was 76% overall (persistent ITP, 81%; chronic ITP, 74%) and 92% after first response (persistent ITP, 92%; chronic ITP, 93%). Nineteen patients (persistent ITP, 7; chronic ITP, 12) maintained platelet counts ≥50x109/L while withholding all ITP therapies for ≥6 months (treatment-free response); all had received romiplostim before treatment-free response. Median duration of treatment-free responses was 12 months (persistent ITP, 12 months; chronic ITP, 11 months).

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In this comprehensive database of romiplostim ITP trials with 468 patient-years of romiplostim exposure, romiplostim was well tolerated, and no immunogenicity or bone marrow issues were identified. Most patients had a platelet response to romiplostim; some achieved a treatment-free response while withholding all ITP therapies. Median treatment duration, tolerability, and platelet responses were similar between children with persistent or chronic ITP at baseline.

Copyright © 2019 The Authors. Published by Wolters Kluwer Health Inc., on behalf of the European Hematology Association.